Semester

Fall

Date of Graduation

2025

Document Type

Dissertation

Degree Type

PhD

College

School of Public Health

Department

Occupational & Environmental Health Sciences

Committee Chair

Michael McCawley

Committee Co-Chair

Eun Gyung Lee

Committee Member

Travis Knuckles

Committee Member

Jeremy Gouzd

Abstract

Thermal Spray Coating (TSC) processes are industrial surface treatment methods used to create coatings for repair, protection, and performance enhancement of components exposed to wear, corrosion, heat, or other harsh conditions. The most commonly used TSC techniques (flame spraying, electric arc spraying, HVOF spraying, plasma spraying, and cold spraying) are used across numerous industries including aerospace, automotive, biomedicine, and energy due to their ability to enhance surface properties such as providing corrosion resistance, wear resistance, and thermal insulation. While TSC techniques have been commercially available for nearly a century, they have undergone continuous development to accommodate more specialized applications, unique materials, and advanced automation. Despite these innovations, the occupational health implications of TSC processes remain underexplored compared to other industrial processes involving similar thermal and particulate emissions, such as welding or additive manufacturing.

Among the various TSC technologies available, Cold Spraying (CS) has emerged as a novel method that differs significantly from conventional TSC processes. CS operates in a solid state by accelerating powder particles to high velocities using a heated, pressurized gas, without melting the feedstock material. CS offers advantages not found in other TSC methods, such as minimal oxidation, retention of feedstock properties, and reduced thermal impact on substrates. Despite its rising popularity, very limited information exists on the emissions generated during CS operations and the potential risks said emissions pose to worker health. Unlike high-temperature TSC methods, CS does not produce metal fumes from vaporization yet still may generate fine and ultrafine particles throughout powder fragmentation, rebound, or erosion mechanisms. These gaps in knowledge regarding TSC emissions, toxicological data, and health outcomes related to TSC emissions, especially CS, need to be addressed.

This dissertation addresses critical knowledge gaps in the occupational health landscape of TSC processes, focusing on CS. The three-chapter format presents a systematic approach to exploring exposure potential and health implications of CS operations. Chapter 1 consists of a scoping review of published literature on TSC-related data on exposure assessments, toxicological data, and health outcomes, along with identifying the gaps in knowledge of these topics in this realm. Chapter 2 presents a controlled laboratory study characterizing particle emissions during CS under various operating conditions using direct-reading instruments and offline samplers. Additionally, a mixed-effect model analysis was conducted to determine which factors (powder type, powder shape, substrate type, transverse gun speed, and carrier gas heat) significantly influence particle emissions. Chapter 3 introduces a methodological approach to transforming multimodal particle size distribution (PSD) data collected during CS operations in a laboratory setting into a usable format that can be inputted into lung deposition software for toxicological interpretation.

Together, these chapters offer a comprehensive overview of what is known in the realm of occupational health in TSCs, the first characterization study of CS emissions, and a methodological approach to translating multimodal PSD data into meaningful estimates of respiratory tract deposition across different exposure scenarios.

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